A nanowire is a wire having at least one dimension, typically a lateral size, constrained to tens of nanometers or less and an unconstrained longitudinal size. Examples of different types of nanowires include metallic (Ni, Pt, Au), semiconducting and insulating; representative materials include, but are not limited to, InP, Si, GaN, SiO2, TiO2, etc.
Typical nanowires exhibit aspect ratios of 1000 or more. As such they are often referred to as 1-dimensional materials. Nanowires have many interesting properties that are not seen in bulk or 3-D materials since electrons in nanowires are quantum confined laterally; and thus occupy energy levels that are different from the traditional continuum of energy levels or bands found in bulk materials. This quantum confinement is exhibited by certain nanowires, such as carbon nanotubes, which results in discrete values of electrical conductance. There are many applications where nanowires may become important in electronic, opto-electronic and nanoelectromechanical devices, as additives in advanced composites, for metallic interconnects in nanoscale quantum devices, as field-emittors and as leads for biomolecular nanosensors.
After many successful reports on the synthesis, characterization and applications of one-dimensional nanostructures of carbon, various other semiconductor materials and metal oxides have attracted much attention in this new emerging field due to their potential applications in nanocircuits, nano-optoelectronic devices and nanosensors etc. Of the several metal oxides, ZnO has received special prominence due to its unique properties such as direct band gap (Eg=3.37 eV), high exciton binding energy of 60 meV, and partial ionic characteristics resulting in no net dipole moment along preferential orientation (c-axis). ZnO is used in sensors, piezoelectric transducers, field emission sources, transparent conducting oxides (TCO's) in solar cells, biomedical applications and surface acoustic wave (SAW) devices.
Nanocrystalline diamond exhibits high hardness, exceptional thermal conductivity, chemical inertness, biocompatibility, and negative electron affinity. These unique properties make NCD a promising candidate for use as a protective coating with excellent tribological properties; a functional platform for biosensors; and structural material for micro-electro-mechanical systems (MEMS). Particularly, diamond electrodes have attracted considerable interest in recent years due to their superb electrical, thermal and electrochemical properties.
After the successful growth and characterization of the ultrananocrystalline diamond (UNCD) films, interest in the application of ZnO for SAW devices on the UNCD films increased. However, due to the large lattice mismatch between (001) plane of ZnO and (111) plane of the diamond lattice, it is very difficult to grow high-quality ZnO films on the diamond substrates. Integration of dissimilar materials is attractive to fully exploit the potential of the material and realize more applications.
While self-assembled hybrid structures of carbon nanotubes and ultrananocrystalline diamond have been successfully synthesized, the success in the integration of carbon based materials with metal oxides has not been studied. There are no reports on hybrid structures of oxide nanowires and nanocrystalline diamond (NCD) films.